In typical telecommunication systems, a site location (e.g., a large building) is electrically connected to a telephone service provider through one or more telephone lines. Typically, each telephone line is made up of a pair of wires or conductors where one of the conductors is known as the tip (T) and the other is known as the ring (R). As such, each telephone line is commonly referred to as a "T/R pair."
For most site locations, the incoming T/R pairs for the site are all routed to a central location, often referred to as a telephone room. T/R pairs corresponding to communications equipment located within the site (e.g., telephones, modems, etc.) are also routed to the telephone room, such that the communication connections between the incoming T/R pairs and the corresponding internal T/R pairs are made through the customer premise equipment ("CPE"). Often the incoming T/R pairs are connected to the internal T/R pairs through the use of standard punch down connection blocks, or "punch down blocks." Thus the telephone room is one location where connections are made between T/R pairs using a punch down block.
Additionally, within site locations connections are made between T/R pairs using punch down blocks. Such T/R pair connections are used to provide extension lines for communications equipment and are also used, for various purposes, in PBX and key systems. Thus, in typical communication systems, there are a number of T/R pair connections that are made through the use of punch down blocks.
An example of a punch down block may be found in U.S. Pat. No. 3,234,498, issued to A. Logan. The punch down block of the referenced patent consists of a plurality of split blade-like metallic terminals arranged side-by-side in rows forming a rectangular array of terminals mounted in an electrical insulating block. The terminals are of the insulation-penetrating clip type which penetrates the insulation of a T or R conductor and tightly clamps and makes electrical contact with the conductor. The terminals are blade-like and are arranged side-by-side in rows so that faces of the terminals lie in a horizontal plane. Punch down blocks of the type referred to are common in the telecommunications industry and take various forms, including the form commonly referred to as a standard M1-50 or 66M1-50 or 66 punch down block.
To protect the communications equipment located within the site, circuit protection devices are often coupled to the input and internal T/R pairs at the telephone room or to the T/R pairs associated with another T/R pair connection, such as a connection associated with an extension line. Such protection devices may take the form of transient surge suppression devices. In many instances the circuit protection devices are adapted to receive the blades of a standard punch down block, such that the circuit protection devices may be coupled to the appropriate T/R pairs via the punch down block. Such circuit protection devices, capable of receiving the blades of a standard punch down block, are referred to herein as "punch down protection modules."
While many punch down protection modules provide acceptable transient over-current or transient over-voltage protection for short-term "lightning-like" transients, they often do not provide protection against various longer-duration electrical phenomena--sometimes referred to as longitudinal over-currents and/or ground equalization currents--that may appear on one of the T/R pairs as a result of a fault current or a ground equalization problem. As a result, such longitudinal over-currents, or other similar electrical phenomena, may pass from one of the T/R pairs to the corresponding T/R pair, thus, damaging the site equipment to which the corresponding T/R pair is attached.
One solution that has been proposed to address this problem is to couple an external choke coil in series with either the input or internal T/R pair. Such external choke coils often result in space-taking and "clumsy" arrangements, in that, the external choke coils require a significant amount of space and separate wiring. This problem can be particularly acute when multiple input and internal T/R lines and thus multiple external choke coils are used. Additionally, the use of external choke coils requires additional installation time and expense.
It is an object of the present invention to overcome the described and other limitations of the prior art and to provide a single, unitary punch down protection module that requires minimal space and provides both transient circuit protection and protection against longitudinal over-currents, ground equalization currents, or other similar electrical phenomena.